This invention relates to circular shaped charges and more particularly to a system and method for making, shipping and assembling a circular shaped charge which facilitates the safe shipping of explosive components.
The use of shaped-charges for cutting tubular goods such as production tubing, drill pipe, or casings used to line wells such as oil and natural gas wells and the like, is well-known in the art. For example, U.S. Pat. No. 3,057,295, issued Oct. 9, 1962 to G. B. Christopher discloses a shaped-charge apparatus for cutting oil well tubing and the like.
Generally, shaped-charges utilized as tubing cutters include a circular, also described as annular or ring shaped, explosive element having a concave surface around its outer circumference. The concave surface normally has a V shaped cross section. The concave surface of the explosive is lined with a thin metal liner which, as is well known in the art, is explosively driven to hydrodynamically form a flat disk shaped jet of material with fluid-like properties upon detonation of the explosive. This jet of viscous material exhibits a good penetrating power to cut tubing. The shaped charge is often manufactured in the form of two identical half charges, top and bottom halves, each comprising explosive material pressed onto a half liner. Two such half charges may be assembled to form a complete circular shaped charge.
Generally, explosive materials such as HMX, ROX, PYX, HNS or PETN are coated or blended with binders such as wax or synthetic polymeric reactive binders such as chlorotrifluoroethylene, sold under the registered trademark NEOFLON by Daikin Industries (formerly available from 3M Corporation under the trademark KEL-F) or a fluoroelastomer sold by DuPont Dow Elastomers L.L.C. under the registered trademark VITON. The resultant mixture is cold- or hot-pressed directly into a shaped-charge case or onto a full or half liner. The resulting shaped-charges are initiated by means of a booster or priming charge in the form of a pellet positioned in the center of the circular main charge and located so that a detonating fuse, detonating cord or electrical detonator may be positioned in close proximity to the priming charge.
The shipment of explosives is carefully regulated by various government agencies, primarily for safety purposes. The regulations impose various levels of restrictions depending upon type of explosive, weight of individual explosive components, total weight in an individual package, relative positioning of multiple explosive components in a single package, types of packaging materials and other factors. It is desirable for the explosives used in shaped charges to meet the requirements for the least restrictive shipping rules both because it reduces the expense and time for shipping and means that the risk of accidents has been minimized.
The present invention provides a structure and methods for making and assembling a circular shaped charge which improves safety in shipping the charge components to a work location. The shaped charge comprises explosive half charges pressed into a desired shape and a separate continuous charge liner or continuous half liners. Each half charge preferably comprises a plurality of segments which may be assembled to form a complete half charge.
In a preferred manufacturing process, explosive segments are individually pressed into final form at the factory. The explosive is preferably mixed with a binder to increase its mechanical strength and ability to be shipped without breakage.
The half charges or segments are preferably separately packaged for shipment. When received at the job site, the individual half charges or segments are assembled with the liner or half liners to form a complete circular shaped charge. The complete circular shaped charge may then be assembled into a tubing cutter tool and used in a well for cutting tubing, drill pipe, etc.